1. Back up your important data ASAP. If you can, use flash drives or an external hard drive--your computer may continue to crash if you attempt to burn CD's.
2. Download Applejack immediately. Applejack is a repair utility that can operate in single-user mode even if you can't boot Mac OS X--if you can keep the computer on long enough for Command-S, you can get to Applejack. http://www.versiontracker.com/dyn/moreinfo/macosx/19596
3. Run Applejack to see if it can fix the problem. This is unlikely but possible.
4. Be prepared for logic board failure or hard drive failure. It sounds like you're on your way there, unfortunately. Since you're in the one year warranty period, Apple will fix that sort of damage for free, but it'll take up to two weeks for them to ship your Powerbook out and get it back to you.

but it'll take up to two weeks for them to ship your Powerbook out and get it back to you.

I've sent my powerbook in twice, once for display and top and bottom case replacement, and another for another display replacement under applecare. Each time it only took 2 days to send it out fix it and ship it back. Gotta love applecare